Composite type magnetic head using composite metallic wire

ABSTRACT

A composite metallic wire includes: an inner layer having a cross-sectional shape of a rough circle; and a metal outer layer having a cross-sectional shape of a rough ring; wherein the composite metallic wire has a diameter of 15 μm or less and an electric resistance of 300 Ω/m or less. A composite type magnetic head using as a coil wire a composite wire comprising: (1) a composite metallic wire comprising: an inner layer having a cross-sectional shape of a rough circle; and a metal outer layer having a cross-sectional shape of a rough ring; wherein the composite metallic wire has a diameter of 15 μm or less and an electric resistance of 300 Ω/m or less, and (2) an insulating coat provided in the outer periphery of the outer layer.

This application is a division of application Ser. No. 08/824,114, filedMar. 26, 1997 now U.S. Pat. No. 6,068,917.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a composite metallic wire which can besuitably used as a coil wire for a composite type magnetic head,particularly, as a coil wire for a high-density magnetic recording headand to a magnetic head using the composite metal wire.

With the spread of computers, an increase of a capacity and a speed upof a magnetic recording apparatus have been rapidly improving.Accordingly, a magnetic head is required to have (1) a smaller size and(2) a lower inductance.

In order to enlarge a valid recording area and improve a runningfollowability of a magnetic recording apparatus, a slider is changedfrom one having dimensions of 4.3 mm×2.9 mm×0.86 mm, which was astandard slider originally, to another one having dimensions of 2.0mm×1.6 mm×0.46 mm, which is a main current slider and called “50%slider”. Further, a slider called “30% slider” is under investigation.

In order to improve a transmitting speed, it is required that afrequency upon reproducing a record. Therefore, it is required that aninductance of a magnetic head is lowered so as to shorten a rise time ofa recording current in a range of high frequencies. For example, in thecase of 600 Mb/in², the inductance is required to be 0.9 μH or less. Inthe case of 700 Mb/in², the inductance is required to be 0.7 μH or less.For reducing an inductance of a magnetic head, it is required that across sectional area of a magnetic path is reduced, for example, athickness of a magnetic core is reduced, thereby causing a problem ofreducing an efficiency of the head. To solve the problem, a magneticpath should be shortened. Specifically, a window for a coil should bemade smaller, thereby reducing an inductance.

However, a window for a coil of a magnetic core is required to be woundby a coil wire with a predetermined number of turns. For example, in thecase of 600 Mb/in², the number is 26, and in the case of 700 Mb/in², thenumber is 24. Therefore, the window is required to have a sizesufficient for the winding. Accordingly, a minimum size of the windowfor a coil depends on a diameter of a wire used for the coil.

FIG. 3 shows a core chip in which a conventional wire is used. The corechip 10 mainly consisting of a trailing core 16 and leading core 18. Acoil 28 made of a wire is wound around a window 12 for a coil formed bythe trailing core 16 and a leading core 18.

The surfaces of the trailing core 16 and the leading core 18 which arefacing to each other are covered with metallic films 22, respectively.Between these films, a magnetic gap 20 consisting of a glass 24 isformed. Incidentally, 26 is an insulating protective tube.

As shown in FIG. 3, a conventional core chip in which a wire is used,the coil has a large diameter. Accordingly, the window 12 for a coilcould not be made smaller, and inductance could not be reduced.

Conventionally, an alloy of copper and silver has been used as amaterial for the wire having a minimum diameter of 22 μm and a maximumtensile strength of 20 g.

It is technically possible to thin down a copper alloy wireconventionally used. However, indeed, a wiring operation is manual, andtherefore, a wire having a low tensile strength has problems of thesnapping of the wire, and the like. Accordingly, the wire is required tohave a tensile strength of at least 20 g. Therefore, it is difficult touse a thin copper alloy wire as a coil wire from the view point ofmass-production.

Accordingly, it is difficult to achieve a memory density of 600 Mb/in²or more by using a magnetic head using a wire such as a conventionalcopper alloy wire.

As a structure of a composite type magnetic head, a core chip embeddingtype is known.

For producing this magnetic head, a track machining is first given, acore chip having a thickness (d) of 50 μm is inserted into a groove forinserting a core chip and tentatively fixed. Then, glass is fused andpoured in the periphery of the track portion so as to fix the core chipto the slider. After that a tentative fixing member in a back portion isremoved, and a resin is poured into the portion to fix the core chip tothe slider. Then, surplus glass on a sliding surface is removed, andsimultaneously, the surface is polished so as to form a gap depth.

A composite type magnetic head thus produced has a structure shown in,for example, FIG. 4.

In FIG. 4, 30 is a non-magnetic housing. In a condition that a core chip29 is fixed to the housing 30, a coil 31 is set so as to form a slider36. To the slider 36 having a coil 31 is connected a suspension 32 forgenerating a force toward a medium. To the suspension is fixed a tube 33for insulating and protecting a lead wire 35. In this condition, amagnetic head 37 is constituted.

The magnetic head 37 floats at a minute intervals on the medium by abalance of a floating force and a pressure 4 from the slider 36 to themedium by the suspension 32. The floating force is generated between asliding surface and the medium. Thus, the magnetic head 37 can move overthe medium of the slider 36 at a high speed.

The smaller and lighter slider 36 is more preferable because aflowability is enhanced against a rough surface of the medium, thefloating is more stable, a magnetic converting property is enhanced, anda speed-up of the movement of the slider 36 over the medium can beachieved. However, a size of the slider 36 is restricted by a size of aslit 34. As seen from FIG. 4, since a wire is wound in a state that theslider 36 slides, the slider 36 is provided with a slit 34 for thewinding. A size of the slit 34 is restricted by a size of a slider 36. Asize of the slit 34 is a maximum restrictive matter in the case that asize of the slider 36 is decreased. Accordingly, making a wire materialfor a coil thinner and making the coil smaller enables tominiaturization of the slider 36, thereby improving a floatingstability.

Thus, it is important to thin down a wire material for a coil in acomposite type magnetic head, too.

SUMMARY OF THE INVENTION

The present invention aims to provide a wire material of a compositemetallic wire the diameter of which is reduced and the tensile strengthof which is enlarged so as to enable a wiring operation.

The present invention aims to provide also a composite type magnetichead which can cope with a memory density of 600 Mb/in² or more by usingthe aforementioned composite wire.

The present invention is intended to solve the above problems.

According to the present invention, there is provided a compositemetallic wire comprising:

an inner layer having a cross-sectional shape of a rough circle; and

a metal outer layer having a cross-sectional shape of a rough ring;

wherein the composite metallic wire has a diameter of 15 μm or less andan electric resistance of 300 Ω/m or less.

The composite metallic wire is preferably provided with an insulatingcoat in the outer periphery of the outer layer.

The composite metallic wire preferably has a diameter of 14 μm or less.

The inner layer is preferably constituted of a wire material having adiameter of 12 μm or less and a tensile strength of 15 g or more.

Further, the inner layer may be composed of a metallic material, acarbonaceous material, or an organic material.

Furthermore, the outer layer is preferably constituted of a materialhaving a specific resistance of 6×10⁻⁸ Ω·m or less.

Furthermore, the composite metallic wire preferably has a tensilestrength of 20 g or more.

According to the present invention, there is also provided a compositetype magnetic head using as a coil wire a composite wire comprising:

a composite metallic wire comprising: an inner layer having across-sectional shape of a rough circle; and a metal outer layer havinga cross-sectional shape of a rough ring; wherein the composite metallicwire has a diameter of 15 μm or less and an electric resistance of 300Ω/m or less, and an insulating coat provided in the outer periphery ofthe outer layer.

Here, a memory density means a product of a track density and a wirerecording density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a composite metallic wire showing anembodiment of the present invention.

FIG. 2 is a front view of a core chip using a composite metallic wire ofthe present invention.

FIG. 3 is a front view of a core chip using a conventional coil.

FIG. 4 is a front view of a magnetic head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a composite metallic wire of the present inventionis constituted of an inner layer 1 having a cross-sectional shape of arough circle and a metallic outer layer 3 having a cross-sectional shapeof a rough ring.

The inner layer 1 is preferably a wire having a diameter of 12 μm orless and a tensile strength of 15 g or more. As a material for the innerlayer 1, there can be used a metal such as tungsten, molybdenum,beryllium copper, brass, platinum, or the like, which can be thinneddown. Among them tungsten is most preferable in view of strength.

A material for the inner layer 1 may be a carbonaceous fiber, a SiCfiber, or an organic fiber, which can be thinned down. As a material ofthe organic fiber, there may be used phenolic resins a polyamidesynthetic fiber such as, nylon 6, nylon 66, and KEVLAR® (an aramidfiber); a polyester synthetic fiber such as poly(ethyleneterephthalate); and a vinyl chloride.

When a metallic fiber having a difficulty in plastic working such astungsten, molybdenum, and the like, has a larger diameter than apredetermined one, it is subjected to electrolytic polishing, or thelike, so as to obtain a predetermined diameter.

A material for the outer layer 3 may be a metal having a specificresistance of 6×10⁻⁸ Ω·m or less, such as Ag, Cu, Au, and the like.

The outer layer 3 is formed by an electrolytic plating when the innerlayer 1 is conductive, and by a nonelectrolytic plating when the innerlayer 1 is not conductive. A thickness of the outer layer 3 isdetermined so that the outer layer 3 has an electric resistance of 300Ω/m or less. Alternatively, a method such as vapor deposition,sputtering, or the like, may be used. The outer layer 3 is generallyformed under the known normal conditions.

As an insulating coat 5, a natural used in the present invention is notparticularly limited as it is long as a material having an insulatingability. For example, a material for insulating a coating of a magnetwire is applicable. As such a material, polyurethane, polyester,polyesterimide, or the like, can be employed. Among them polyurethane issuitable which can be soldered without removing the insulating coat.When one of the aforementioned insulating coats covering the compositemetallic wire sustains damage upon winding operation surface of aninsulating coat is preferably coated with a lubricating resin such asnylon, thereby enabling to avoid a damage.

FIG. 2 shows a core chip in which a coil wire of the present inventionis used. The constitution is the same as that of FIG. 3. A core chip 10is constituted mainly of a trailing core 16 and a leading core 18. Thetrailing core 16 and the leading core 18 form a window 12 for winding awire, around which a coil 14 of a wire is wound with a predeterminednumber of turns.

As obvious from a comparison of structures in FIGS. 2 and 3, a core chipof the present invention using a coil wire having a smaller diameter hasa coil 14 having a larger number of turns of wire around the window 12in comparison with a conventional core chip having the same size of thewindow 12.

A composite type magnetic head of the invention can be produced by usingthe composite metallic wire of the present invention so as to have astructure like the one shown in FIG. 4.

That is, a core wire having a small diameter of the present invention iswound with the same number of turns as in a conventional core head, acore chip 29 and a slit 34 can be made smaller than those of theconventional core head, thereby enabling to miniaturize a slider 36.

As described above, according to a composite type magnetic head using acomposite metallic wire of the present invention having a small diameterand a tensile strength of predetermined value or higher, miniaturizationand lowering of an inductance can be achieved.

EXAMPLE Examples 1-11

A tungsten wire (inner layer) having a diameter of 15 μm and a length of1000 m was subjected to electrolytic polishing by a well-known method ora drawing so as to obtain a wire having a diameter of 8-12 μm.

Subsequently, on the obtained wire was formed an outer layer by aelectrolytic plating in a well-known method using a copper having athickness of 1.5-3.5 μm.

Then, an insulating coat made of polyurethane was formed on the outerlayer so as to have a thickness of 2.5, 3.0 or 3.5 μm so as to obtain acomposite metallic wire having the insulating coat and having a diameterof 19 or 22 μm.

The results are shown in Table 1.

For example, in the case of Example 1, a tungsten wire was subjected toelectrolytic polishing to obtain a diameter of 8 μm. Subsequently, theouter layer made of copper having a thickness of 2.5 μm was formed.Then, an insulating coat made of urethane and having a thickness of 3.0μm was formed on the outer surface so that a composite metallic wirehaving the insulating coat might have a diameter of 19 μm.

The composite metallic wire having the insulating coat had a tensilestrength of 20 g and an electric resistance of 190 Ω/m.

TABLE 1 Thickness of Diameter of Diameter of Thickness of Diameter ofinsulating Composite Wire Electric Tensile inner layer outer layerComposite Wire coat w/insulating Resistance Strength (μm) (μm) (μm) (μm)coat (μm) (Ω/m) (g) Example 1 8 2.5 13 3.0 19 190 20 Example 2 9 2.0 26023 Example 3 8 3.0 14 2.5 150 22 Example 4 9 2.5 180 25 Example 5 10 2.0230 30 Example 6 11 1.5 290 32 Example 7 8 3.5 15 3.5 22 130 23 Example8 9 3.0 155 27 Example 9 10 2.5 170 33 Example 10 11 2.0 210 35 Example11 12 1.5 260 40

Comparative Example 1

A tungsten wire (inner layer) having a diameter of 15 μm, and a lengthof 1000 m was subjected to a drawing so as to obtain a tungsten wirehaving a diameter of 10 μm.

Subsequently, an outer layer made of copper and having a thickness of1.5 μm was formed on the wire by an electrolytic plating.

Then, an insulating coat made of polyurethane and having a thickness of3.0 μm was formed to obtain a composite metallic wire having theinsulating coat. The composite metallic wire having the insulating coathad a diameter of 19 μm. The other conditions were the same as inExample 1.

The results are shown in Table 2.

The composite metallic wire having the insulating coat had a tensilestrength of 25 g and an electric resistance of 330 Ω/m.

Comparative Example 2

A tungsten wire (inner layer) was subjected to electrolytic polishing soas to obtain a tungsten wire having a diameter of 13 μm.

Subsequently, an outer layer made of copper and having a thickness of1.0 μm was formed on the wire by an electrolytic plating.

Then, an insulating coat made of urethane and having a thickness of 3.0μm was formed on the outer layer so as to obtain a composite metallicwire having the insulating coat and having a diameter of 21 μm. Theother conditions were the same as in Example 1.

The results are shown in Table 2.

TABLE 2 Thickness of Diameter of Diameter of Thickness of Diameter ofinsulating Composite Wire Electric Tensile inner layer outer layerComposite Wire coat w/insulating Resistance Strength (μm) (μm) (μm) (μm)coat (μm) (Ω/m) (g) Comparative 10 1.5 13 3.0 19 330 25 Example 1Comparative 13 1.0 15 3.0 21 360 50 Example 2

From Tables 1 and 2, the followings are understandable.

(1) From the comparison of Comparative Example 1 to Example 6, it isknown that an electric resistance of 300 Ω/m or less cannot be obtainedwhen a cross-sectional area of an outer layer is small even if the outerlayer has the same thickness.

(2) When a thickness of an outer layer is increased and an inner layeris decreased so as to reduce the electric resistance, a tensile strengthof the composite metallic wire is reduced.

(3) When tungsten wire is used for an inner layer, a lower limit of thediameter is 8 μm so as to satisfy a tensile strength of 20 g or more andan electric resistance of 300 Ω/m or less.

Reference Examples 1-7

Incidentally, a tungsten subjected to only electrolytic polishing wasmeasured for an electric resistance. The results are shown in Table 3.

As shown in Table 3, an electric resistance of 300 Ω/m or less cannot beobtained by using only an electrolytically polished tungsten.

TABLE 3 Diameter Thickness Thickness of Electric Tensile of inner ofouter insulating coat resistance strength layer (μm) layer (μm) (μm)(Ω/m) (g) Reference 8 — — 1096 25 Example 1 Reference 9 — — 865 32Example 2 Reference 10 — — 700 39 Example 3 Reference 11 — — 580 45Example 4 Reference 12 — — 487 56 Example 5 Reference 13 — — 414 66Example 6 Reference 14 — — 357 76 Example 7

Reference Examples 8-12

As a withstand voltage property in a case that a wire is wound around acore chip having a thickness of 35 μm, there were obtained thicknessesof insulating coats each satisfies a condition of over 25 MΩ at 50 V,over 1000 MΩ at 100 V, and over 1000 MΩ at 200 V.

The results are shown in Table 4.

As obvious from Table 4, it is necessary for an insulating coat to havea thickness of 2.5 μm or more. In this case, a composite metallic wiresame as in Example 7 was used, and polyurethane was used as aninsulating coat.

TABLE 4 Diameter Dia- Thick- of comp- Ratio of Dia- Thick- meter of nessof osite passing meter ness comp- insula- wire w/ voltage of inner ofouter site ting insulating withstand layer layer wire coat coat test of(μm) (μm) (μm) (μm) (Ω/m) wire (%) Reference 1.0 17 30 Example 8Reference 2.0 19 75 Example 9 Reference 8 3.5 15 2.5 20 100 Example 10Reference 3.0 21 100 Example 11 Reference 3.5 22 100 Example 12

Example 12

A composite type magnetic head was produced by using a compositemetallic wire of Example 1.

As a magnetic core, Mn—Zn ferrite which was grown by a solid phasereaction method was used. Metallic films between gaps are formed byFe—Ta—N films each having a thickness of 2 μm or 5 μm. A compositemetallic wire produced in Example 1 was used as a coil for a magnetichead. FIG. 2 shows a core for a 50% slider having 700 Mb/in². Thecomposite metallic wire was wound 26 times to the core having athickness of 35 μm and a window having a size of 0.10 mm×0.20 mm withoutbreaking of the wire.

The obtained composite type magnetic head has an inductance of 0.6 μH.When a conventional cupper alloy wire, i.e., a wire having a diameter of22 μm was used, the wire could be wound only 17 times, and apredetermined number of winding could not be obtained.

As described above, according to the present invention, there wasobtained a composite metallic wire having a diameter of 15 μm or lessand a tensile strength of 20 g or more for a wiring operation.Accordingly, a window for winding a wire can be miniaturized, andtherefore, a magnetic head having a high memory density can be obtained.

Further, according to the present invention, there was obtained amagnetic head having a low inductance.

What is claimed is:
 1. A composite type magnetic head having a coilwire, said coil wire comprising a composite metallic wire whichcomprises: a core having a cross-sectional shape of a rough circle andbeing a member selected from the group consisting of a metallic fiber, acarbonaceous fiber, an SiC fiber and an organic fiber; and a metal outerlayer having a cross-section shape of a rough ring; wherein thecomposite metallic wire has a diameter of 15 μm or less and anelectrical resistance of 300 Ω/m or less, an insulating coat provided onthe outer periphery of the outer layer.
 2. A composite type magnetichead according to claim 1, wherein the core has a diameter of 12 μm orless and a tensile strength of 15 g or more.
 3. A composite typemagnetic head according to claim 1, wherein the outer layer isconstituted of a material having a specific resistance of 6×10⁻⁸ Ω·m orless.
 4. A composite type magnetic head according to claim 1, whereinthe composite metallic wire has a tensile strength of 20 g or more.
 5. Acomposite type magnetic head according to claim 1, wherein said core isa member selected from the group consisting of tungsten, molybdenum,beryllium copper, brass, platinum, phenolic resins, nylon 6, nylon 66,aramid, poly(ethylene terephthalate) and vinyl chloride.